1. Field of the Invention
The present invention relates to a stepping motor control circuit and an analog electronic timepiece which uses the stepping motor control circuit.
2. Background Art
Conventionally, a stepping motor having the following constitution has been used in an analogue electronic timepiece or the like. The stepping motor includes a stator which has a rotor accommodating hole and a positioning part for deciding a stop position of a rotor, the rotor which is arranged in the rotor accommodating hole, and a coil, wherein an AC signal is supplied to the coil so that a magnetic flux is generated in the stator thus rotating the rotor, and the rotor is stopped at a position corresponding to the positioning part.
Conventionally, as a method of controlling the above-mentioned stepping motor, a following correction drive method has been adopted (see JP-B-61-15385 (patent document 1)). In driving a stepping motor with a main drive pulse, whether the rotor is rotated or not is detected by detecting an induction signal generated in the stepping motor, and the stepping motor is driven by changing the main drive pulse to a main drive pulse having a different pulse width or by forcibly rotating the stepping motor with a correction drive pulse having a larger pulse width than the main drive pulse corresponding to the result of detection of whether or not the rotor is rotated.
WO2005/119377 (patent document 2) discloses a method of controlling a stepping motor in which, in addition to the detection of an induction signal in the same manner as patent document 1, energy of a main drive pulse is made small when a detection time of the induction signal is earlier than a reference time and energy of the main drive pulse is made large when the detection time of the induction signal is later than the reference time so that the stepping motor is rotatably driven with the main drive pulse corresponding to a load at the time of driving the stepping motor whereby a consumption current is lowered. Due to such a constitution, the method enables a more accurate pulse control.
However, when the stepping motor is driven with a main drive pulse having a small drive force, there may be a case where the energy of the main drive pulse is small so that the energy balances with a load whereby a rotor is stopped at a middle position where the rotor is not rotated by 180° (intermediate stopping). Accordingly, the techniques disclosed in patent documents 1, 2 cannot cope with drawbacks relating to the intermediate stopping.
On the other hand, JP-A-58-68684 (patent document 3) discloses the invention in which an intermediate stopping state is detected in response to an induction signal generated by the rotation of a rotor. However, the invention adopts the constitution where the intermediate stopping is detected by making use of the finding that an induction signal in the forward direction is not generated in the intermediate stopping state and hence, there exists a drawback that the detection accuracy is poor.
JP-A-2004-260875 (patent document 4) and JP-A-2002-354893 (patent document 5) disclose the inventions where an induction signal which is generated by the rotation of a rotor is detected by another detection resistance. However, these inventions aim at the prevention of detection of an induction signal during a mask period and hence, these inventions are irrelevant to the solution of drawbacks on intermediate stopping.